In large slaughterhouses which are designed for processing poultry, for example chickens; transport systems occur in current practice with many thousands of carriers in a chain. Slaughter lines are known with 15,000 to even 30,000 carriers in a single chain, which may be kilometres long. Between adjacent carriers, different types of chain elements are present, for example one or more links of a chain or a piece of cable, steel wire or the like, which interconnect the carriers.
A plurality of transport systems are often present in slaughterhouses, wherein it occurs that a part of a poultry item held by a carrier in a first transport system is separated and the separated part of the poultry item is transferred to a carrier which forms part of a second transport system.
For example in this situation, it is important during the slaughter process to know the location of the carriers in each of the transport systems. It can thus occur that an inspection station is set up along the second transport track, where a veterinary inspection of passing separated poultry item parts takes place. If a poultry item part is then rejected, it is desirable, and sometimes required, that the associated poultry item part which is still located in the first transport system is also rejected and is treated as such, for example is removed in a reject station. The slaughterhouse installation must then be able to locate the relevant carrier in the first transport system.
In order to be able to locate the carriers in the transport system, as presently used in slaughterhouses, location means are present which can determine at least the position of the chain of carriers in relation to the track.
In a known design of these location means, a single identifiable chain element is present in the chain which has an identification mark, said chain element being referred to as the reference chain element, and the remaining chain elements in the chain are designed as unidentifiable. An identification sensor is then set up along the track to detect the identifiable reference chain element.
The known location means further comprise a counting device set up at a position along the track, usually near the identification sensor, to count the carriers which pass following the passage of the reference chain element.
Furthermore, the known location means comprise electronic memory means with a memory table in which at least one memory field is present for each carrier, wherein the location means record a variable in a memory field for each carrier representing the number of carriers counted by the counting device since the passage of the reference chain element.
In the known transport system described above, a serial number is, in a manner of speaking, allocated to each carrier, starting from the reference chain element. In practice, the memory table comprises, for each carrier, along with the memory field with the serial number of the carrier, also one or more memory fields in which other information can be stored. For example, data relating to the relevant product can also be stored in a memory field of this type, such as the weight or the like.
In an embodiment generally known in practice, the carriers are designed as trolleys which can be moved along a guide rail, with running wheels which engage on the rail. Furthermore, each carrier is provided with a receiver part to receive a slaughter animal or one or more parts thereof.
It is known for a sensor to be set up along the guide rail which is operated under the influence of a passing trolley of a carrier. The reference chain element is then obtained in a known design by placing a bridge piece, in practice a spring, between the running wheels of two adjacent trolleys, said spring operating the relevant sensor as if it related to the passage of a trolley. This longer operating period compared with the passage of a normal trolley is electronically identified and the reference chain element is thus detected in the chain. Furthermore, the sensor performs the counting of the passing trolleys and therefore the carriers. It is known for the sensor to be designed as an element which can be mechanically moved by the passage of a running wheel and which cooperates with an electronic detector, for example an inductive detector.
In a different known variant, an optical sensor which detects each passage of a carrier is placed along the guide rail. An additional chain element is set up between two adjacent carriers in the chain, which can be detected in the same way as a carrier by the optical sensor. The passage of this additional chain element can easily be determined on the basis of the shorter time lapse between successive detections, whereby the reference chain element is then defined.
The transport systems described above essentially operate satisfactorily in slaughterhouses.
However, a problem occurs, for example, in the event of a power failure. This power failure can affect the drive means of the chain and/or the identification sensor and/or the electronic memory means. As a result, even if no apparent problems have occurred within the location means, uncertainty arises concerning the position of the chain in relation to the track and therefore the location of the carriers and products carried thereby in relation to the track and the associated stations.
In terms of food safety, uncertainty of this type in a slaughterhouse for, for example, poultry, is undesirable.
In order to eliminate this uncertainty, in the known transport system the chain is moved on in a “restore routine” until the single reference chain element is again detected by the identification sensor. During this “restore routine”, no new products may of course be added, products removed or actions carried out.
It will be clear that, in the case of a long chain, as described above, the duration of the “restore routine” may be unacceptably long.
Another problem with long chains relates to the loss of a carrier, for example due to a carrier breaking off from the chain. In the present approach, a loss of this type is identified at an undesirably late stage, and a large number of the slaughter animals or parts thereof located in the carrier may possibly have to be rejected on food safety grounds.
Finally, as a result of the great length of the chain, in the event of an emergency stop or the like, the carriers may move back against the direction of transport because the chain had been stretched during operation and this stretch is then released. As a result, the location means may, in a manner of speaking, perform a counting error.
An obvious solution to the aforementioned problems is to design all carriers as identifiable carriers and to provide each carrier with a unique identification mark. Each carrier can then possibly be designed to be provided with a remotely readable electronic transponder with a unique code, or to be provided with a readable graphical code, for example a barcode.
Although these solutions are appropriate for fast location of carriers in the chain, they have unacceptable disadvantages. For example, the cost price of the transponders is too high to provide all carriers with a transponder. A disadvantage of readable graphical codes on each of the carriers lies in the reliable reading of these graphical codes with a high reading frequency. In particular, moisture and condensation may hinder the reading and the graphical codes will quickly deteriorate.
The aforementioned disadvantage of the known approach for determining the position of the chain in relation to the track also comes to the fore in connection with the “stretching out” of the chain. As mentioned, the chain may be very long and because, almost inevitably, the chain stretches during use (for example through wear), chain elements, including carriers, are in practice removed regularly, for example weekly, from the chain in order to compensate for the stretch. Also, as a result of faults or breakage of the chain, carriers are in practice removed from the chain by maintenance personnel. As a result of the removal of the chain elements, the chain as defined in the memory table no longer corresponds to the actual chain, so that a restore routine is required in order to re-establish said correspondence.